1. Field of the Invention
The invention relates to a device for the alignment of a guide template permitting to perform a resection of the distal femur in one-compartment joint replacements.
2. Description of Related Art
In surgical operations, a mechanical tool guidance by means of cutting guide heads or drill templates and saw guide slots is often indispensable for the realization of an exact osteotomy or resection of bone, as necessary, for example, for the implantation of a joint endoprosthesis.
A device including a plurality of precision instruments for realizing saw cuts in bone, particularly in the distal part of the femur adjoining the knee-joint and in the tibia, is known from U.S. Pat. No. 4,524,766 to Petersen. The different resection cuts to be made on the femur and on the tibia are realized with this known device by means of different precision instruments that are sequentially attached to the femur or to the tibia. These known precision instruments serve for aligning the templates, which are subsequently screwed onto the bone. After that, the precision instruments may be removed and the cuts may be performed by the surgeon.
Another device of this type is known from EP 322363 to Wehrli. With this known device, the guide templates are equally aligned using a previously affixed equipment of instruments and are then screwed onto the bone. The disclosed equipment of instruments includes two attachment arms laterally fixed on the tibia by means of two Schanz screws, and a measuring rod preferably fastened to the attachment arms at a distance of about 10 cm from the tibial axis. The measuring rod is provided with a guide rail on which the template is displaceably mounted so as to be capable of being moved with great precision into the desired position.
The known devices mentioned above both suffer from the disadvantage of having a relatively big volume, which necessitates big openings to be made in the soft tissues surrounding the joint.
The invention is intended to provide a remedy for this. It is accordingly an object of the invention to provide a device for aligning guide templates, said device having a minimum volume.
The object to be achieved by the invention is to make it possible, by its application, to restore the natural geometry of the knee. Particularly in connection with a one-condyle (one-compartment) knee replacement (sliding prosthesis) it is of great importance to optimally adapt the prosthesis to the natural circumstances. In doing so, particular attention must be paid to the line of the knee-joint and to the ligamentous apparatus.
According to the invention, this object is achieved by means of a device for aligning a guide template permitting resection of the distal femur in connection with one-compartment joint replacements.
The device according to the invention comprises essentially two support members each having one support surface that can be arranged so as to lie in one plane and are designed to bear each against one condyle of a femur, at least one rod-like transverse coupler arranged parallel to the transverse axis, which, in its end portion, is connected to the first support member and which is connectable to the second support member, the transverse axis extending parallel to the plane. The device according to the invention further comprises a guide template. The guide template is displaceable parallel to the plane and relative to the second support member by means of positioning means and is releasably lockable thereon in any desired position. In addition, the second support member is arranged so as to be secured against rotation relative to the transverse axis and displaceable coaxially to the transverse axis on the at least one transverse coupler and equally lockable in any desired position, so that the support surfaces may be adapted individually to the varying distances between the medial and lateral condyles of different femora.
In the preferred embodiment of the device according to the invention, the second support member comprises an insert including the second support surface. The insert is displaceable coaxially to a central axis extending perpendicularly to the plane and relative to the second support member. Due to this configuration, the insert, which includes the second support surface, may be displaced parallel to the plane, which permits an individual adaptation of the insert carrying the second support surface as may be necessary, for example in the case of a heavily worn medial or lateral condyle.
Preferably, the second support member includes a bore extending parallel to the central axis and provided with an internal screw thread, so that the insert is displaceable coaxially to the central axis by means of a set screw, which may be screwed into the internal screw thread.
In another embodiment of the device according to the invention, the device comprises a first transverse coupler and a second transverse coupler. The second support member is provided with two parallel bores for receiving the transverse couplers, so that the second support member is displaceable on the transverse couplers so as to be secured against rotation about the transverse axis and is lockable by means of a first locating screw.
In yet another embodiment of the device according to the invention, the positioning means comprise at least one rod segment of the transverse coupler projecting over the second support member on the side opposite to the first support member, and a second locating screw, so that the guide template is displaceable coaxially to the transverse axis so as to be secured against rotation about the transverse axis and is releasably lockable by means of the second locating screw. In this embodiment, the guide template is moved close to the femur from a medial or lateral position.
In another embodiment of the device according to the invention, the positioning means comprise at least one longitudinal carrier arranged parallel to a longitudinal axis and connected to a second support member, as well as a second locating screw. The longitudinal axis extends parallel to the plane and perpendicularly to the transverse axis. By displacing the guide template on the at least one longitudinal carrier, it is possible to move the template close to the femur from a ventral position.
The advantages achieved by the present invention consist essentially in the fact that due to its small volume the device according to the invention makes it possible to keep small the incisions that have to be made in the soft tissues surrounding the joint. By making it possible to use a minimally invasive surgical technique, only a small skin incision is required, which means that patients will lose smaller amounts of blood and they will recover more rapidly while feeling less pain.
In addition, there is no need for an intramedullary opening of the femur, and thus no risk of thrombosis formation nor of a wound that might start bleeding again.
A further advantage resides in the fact that fewer surgical instruments are needed, which simplifies the surgical technique and permits the operating room staff to work with a more light-weight case of instruments. In addition, fewer operation steps are necessary, which reduces the time spent on the individual surgical interventions.